Theme authors: I've seen a lot of this type of code in some themes.
echo get_avatar( get_comment_author_email(), '60' );
That code is wrong. You should have used this instead:
echo get_avatar( $comment, '60' );
get_avatar is a relatively smart function. If you pass it an email address, then it gets the avatar for that email address. But, if you pass it a whole comment object, then it knows how to deal with that properly too. And you really want to pass it the whole object.
Why? Because get_avatar is not limited to getting just gravatars. A plugin might hook a filter in, and recognize when it might be appropriate to get a different sort of avatar, such as one from Twitter or Facebook or some such thing. And if you just passed the email, then the plugin can't see the whole comment, including that oh-so-useful comment-meta.
So do us all a favor. Pass in the whole object. Don't try to be all clever and pass in only the email address. Let the upstream code take care of that for you.